(1) Field of the Invention
The present invention pertains to an adjustable spring grounding pin for grounding three separate parts of an electrical device, for example two end shields and a stator of an electric motor. In particular, the invention pertains to a grounding pin that automatically adjusts its circumferential dimension to provide a tight grounding fit between aligned holes of different interior diameters in end shields and a stator of an electrical device as the grounding pin is driven into the aligned holes.
(2) Description of the Related Art
An electrical device such as an electric motor typically includes the basic component parts of a stator, a pair of end shields mounted over axially opposite ends of the stator, and a rotor. The rotor is positioned in a center bore of the stator with opposite ends of the rotor shaft being mounted for rotation in bearings or bushings in the opposite end shields of the motor.
FIG. 1 shows the basic construction of an electric motor of the type commonly used in household appliances. The motor is comprised of the pair of end shields 12, 14 containing the stator 16. The rotor (not shown) is positioned inside the stator 16 and the end shields 12, 14 support the opposite ends of the rotor shaft 18. On the particular motor shown, each of the end shields 12, 14 has four legs 22, 24 that extend over the peripheral edges of the stator laminations. The distal ends of the legs are secured together by adhesive or by other equivalent means.
Where motors of the type shown in FIG. 1 are employed in household appliances such as dishwashers, clothes washers and clothes dryers, it is very important that the electric motor be properly grounded to protect users of the appliance. One of the motor end shields 12, 14 is usually provided with a ground terminal that is electrically connected to a ground connection of the appliance. The ground connection of the appliance in turn is grounded through a three-prong outlet plug or through a separate ground, for example a ground connection to a cold water pipe of the household.
Component parts of the motor, i.e., the end shields 12, 14 and the stator 16 are often ground connected together by a ground pin 26 that is received in aligned holes in the stator and the end shields. The prior art ground pin 26 is a conductive pin of solid metal having a cylindrical exterior surface and flat circular end surfaces. The pin is usually constructed of a harder metal than that of the end shields and stator laminations to enable the pin to be driven into the stator hole without bending the pin. The ground pin 26 is often installed by first drilling or reaming holes through the soft metal of the end shield legs 22, 24 and into the harder metal of the laminations of the stator 16. To provide grounding contact with both end shields, the grounding pin hole 28 is usually drilled between mating surfaces of the legs, as shown in FIG. 1. The pin 26 would then be manually pressed or hammered into the aligned holes.
This prior art method of grounding motor parts was found to be disadvantaged in that, because the metal of the end shields, and in particular the end shield legs 22, 24, is usually softer than the metal of the laminations of the stator 16, when the hole is formed through the end shield legs and into the stator it would often result in the hole 28 through the end shield legs being slightly larger than the hole 32 formed in the stator. This would occur due to the material of the end shield legs being softer than the material of the stator laminations, and also due to the positioning of the ground pin hole, the hole being drilled through the two mating surfaces of the end shield legs and then into the stator. The dimension of the hole 32 drilled into the stator would be chosen to provide a tight friction fit of the ground pin 26 in the stator hole. If the hole 28 through the end shield legs is larger than the stator hole 32 by 0.006 of an inch, with the ground pin outer diameter being sized to fit tightly into the interior diameter of the stator hole, it is possible that the ground pin would not make contact with the end shield legs or would only make sufficient grounding contact with one of the end shield legs, resulting in the motor not being grounded or only one end shield of the motor being grounded with the possibility of the opposite end shield being live. In order for the motor to have a proper ground, the ground pin 26 must make contact with the stator and both end shields at all times.